1. Field of the Invention
The present invention relates to a digital video receiver, a digital video receiving method and the like used for a conditional access system (CAS), and for instance, to the digital video receiver, digital video receiving method and the like used for cable television, satellite broadcasting and the like.
2. Related Art of the Invention
In recent years, a conditional access system (CAS) is widely used for cable television, satellite broadcasting and the like as a method of exclusively broadcasting to specific viewers.
For instance, a scramble signal is added to a broadcast wave in advance, and in the case of only broadcasting to the specific viewers such as pay-TV, a device for canceling the scramble signal (an STB or the like) is provided only to subscribers. If such a measure is taken, the subscribers can view the pay-TV by using the STB. However, non-subscribers cannot cancel the scramble signal so that they can receive but cannot view a broadcast to which the CAS is applied.
Encryption is differently performed by using a different scramble key to each individual channel so as to allow only the channel under subscription to be viewed even in the case of the STB being possessed.
In the United States, a CableCARD is used as the method of the CAS these days.
FIG. 15 shows a block diagram for describing a mechanism of decryption process of the STB in the CAS using the CableCARD.
An STB 100 is the STB for cable TV installed in each individual household, and an H/E (Head End) 101 is a cable TV station for instance.
A CableCARD 102 is a PC card of the PCMCIA standard, and includes a CAS module 104 for decrypting the scramble key and a descrambler 105 for descrambling a broadcast signal.
To decrypt the scramble key, two kinds of information of an ECM (Entitlement Control Message) and an EMM (Entitlement Management Message) are necessary. The ECM is information per program, and the EMM is information per subscriber.
On the STB 100's body side, a card slot of the PCMCIA standard is provided, and the CableCARD 102 is inserted into the card slot. If the CableCARD 102 is not inserted, the STB 100 cannot descramble the broadcast signal so that viewing is impossible.
As there is the descrambler 105 in the CableCARD 102, there is no need to deliver the scramble key between the CableCARD 102 and the STB 100.
A video/audio output control portion 103 passes a CA_PMT having descriptors other than a CA descriptor deleted from a PMT (Program Map Table) received in-band to the CAS module 104 of the CableCARD 102.
The CAS module 104 extracts the ECM from the CA_PMT passed from the video/audio output control portion 103, and also extracts the EMM required by the STB 100 out of data including information on multiple different EMMs received from OOB. And the CAS module 104 decrypts the scramble key by using a master key possessed in the CableCARD 102 in advance and the extracted ECM and EMM so as to pass the decrypted scramble key to the descrambler 105.
And the descrambler 105 descrambles the broadcast signal by using the scramble key and passes it to the video/audio output control portion 103. As descrambled video data is outputted from the video/audio output control portion 103, the user can view that broadcast program.
Here, the relation between the PMT and the ECM will be described. FIG. 16 is a diagram showing the relation between the PMT and the ECM.
The PMT is a table equivalent to one channel, and a PAT (Program Allocation Table) transmitted in-band includes PIDs of all the channels of PMT. And the PMT includes the PID of a packet including the ECM together with the PID of video data and audio data.
A stream identifier (stream_type) can specify the packet including the ECM out of the PMT. However, the stream identifier is different depending on a CA vendor. The structure of the packet including the ECM has not been disclosed.
It is not possible to extract the ECM out of the stream without having information on a transmitting side, such as the stream identifier specifying the packet including the ECM and the structure of the packet including the ECM.
In the case of the CAS before using the CableCARD, the ECM could not be extracted and the scramble key could not be decrypted without knowing the information on the transmitting side. Therefore, a receiver could not be manufactured without knowing the information on the transmitting side.
As for the CAS using the CableCARD 102 shown in FIG. 15, the STB 100 has only to extract the CA_PMT out of the PMTs and pass it to the CableCARD 102 as a decryption process. The process of extracting the CA_PMT is a process that can be performed just by using the disclosed information.
To be more specific, in the case of the CAS using the CableCARD 102, the CableCARD 102 performs the decryption process. Therefore, it is now possible to manufacture the STB 100 without knowing such information on the transmitting side as described above.